Cellulose-reactive and cellulose non-reactive sizes are used widely for sizing paper during its manufacture. Because these sizes are most frequently water-insoluble, they are generally used in the form of aqueous dispersions so that they can be readily handled in the aqueous paper making environment.
Surfactants, i.e., materials typically containing both oil soluble hydrocarbon chains and water soluble polar groups, are generally not used as dispersants for paper size dispersions because they tend to exhibit an anti-sizing effect, i.e. they reduce water resistance. Conventional surfactants generally have one hydrophilic group and one hydrophobic group. Recently a class of surfactants having at least two hydrophobic groups and at least two hydrophilic groups has been introduced. These have been found to be unexpectedly effective when compared to conventional surfactants (Rosen, M. J., Chemtech, March, 1993, pp. 30-33; and Menger, F. M. & Littau, C. A., J. Am Chem. Soc., 1993, 115, pp. 10083-10090). These have become known in the literature as "gemini surfactants".
Gemini surfactants are disclosed in U.S. Pat. Nos. 5,643,864, 5,710,121, 5,789,371, 5,811,384 and 5,863,886, the disclosures of all five of which are hereby incorporated herein by reference in their entireties. Further examples of gemini surfactants are disclosed in International Publication Nos. WO 95/19955, WO 98/15345, WO 98/15346, WO 98/23365, WO 98/37062 and WO 98/45308.